iM ^ r :^ 



of the order Acarina have the whole body fused into 

 a single piece, and are peculiar too in going through 

 a very different, six-legged larval stage followed by 

 transformation into the eight-legged adult. 



Ticks are mostly larger than mites, and live as par- 

 asites on land-dwelling vertebrate animals. Mites in- 

 clude many that are helpful to man through their 

 predatory habits, eating the eggs of plant lice 

 (aphids), attacking insects and nematode worms in 

 the soil, prowling over the surface of plants and of 

 the ground, and hunting even in shallow ponds. Most 

 mites are external parasites, particularly in larval 

 stages. Water striders and damsel flies are often 

 found carrying on their bodies little red lumps that 

 are the blood-sucking immature individuals of the 

 big predatory red mites found swimming in ponds or 

 along the shore ( Plate 115). 



When a parasitic mite or tick feeds, it thrusts its 

 whole head into the skin of the victim. There the 

 parasite is held in place through use of a dartlike an- 

 chor located just below its mouth. In ticks the outer 

 surface of the anchor bears recurved teeth, and these 

 hold so firmly that a pull on the body of a tick is 

 likely to break oft its head in the wound rather than 

 remove it. In mites the anchor is smooth on the out- 

 side, allowing the parasite to be brushed oflf quite 

 easily. 



The mite affecting most people directly is the chig- 

 ger, usually a member of the genus Troinbiciila. In 

 the Old World these unpleasant creatures are called 

 harvest mites. They lie in wait upon vegetation un- 

 til a vertebrate animal brushes against the plant. 

 Then anywhere from one to a hundred may be 

 "painted on," and promptly begin spreading over the 

 skin. At a chosen site, each mite bites and discharges 

 into the wound a drop of digestive agent which opens 

 a tubular path far enough into the skin to enable nu- 

 tritious lymph to well up and provide the mite with a 

 meal. Soon the chigger drops off of its own accord, 

 seldom remaining on the skin for more than from 

 one to seven days. On the ground it completes its de- 

 velopment and, if a female, eventually mates and lays 

 a batch of eggs from which a new generation of young 

 ascend a grass stalk and wait for a host to pass. 



The action of a chigger is intensely irritating, lead- 

 ing the host (whether man or rat or quail or snake) 

 to scratch vigorously, often breaking the skin and ad- 

 mitting serious infections. The extent of distraction 

 from mite bites can be evaluated on domestic fowl 

 in a hen house infested with the chicken mite Der- 

 manyssiis gallinae. The hens spend so much time 

 scratching that they feed less frequently, become 

 malnourished, and cease to lay reliably. 



Mite pests seem to be found on every hand. The 

 "seven-year-itch" is caused by the itch mite Sarcop- 

 tes scabiei of man and hogs. This creature burrows 

 under the skin and reproduces there. Related mites. 



A mother scorpion Titijus sernilatiis, with newborn 

 young clinging to her back, .'■lands safely under the 

 arch of her sting-tipped abdomen. { Switzerland. Oth- 

 niar Danesch ) 



The whip scorpion Stegophrynus has a body about 

 IV2 inches long. It is harmless to any creature too 

 large to be crushed between the first pair of append- 

 ages. ( Singapore. M. W. F. Tweedie ) 





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